Most blinds that don't fit right weren't a bad product — they were measured wrong before they were ever ordered.
Measuring for custom blinds and shades isn't difficult, but a handful of mistakes account for most of the fit problems we see: measuring the old blinds instead of the window, measuring only one spot on the window, ignoring depth and obstructions, taking your own deductions instead of letting the manufacturer handle them, and assuming windows that look alike are actually the same size. Each one is easy to avoid once you know to watch for it. This guide walks through all five, along with what to do instead, and our full measuring guide covers the complete step-by-step process if you're starting from scratch.
1. Measuring the Old Blinds Instead of the Window
If you're replacing an existing blind, it's tempting to just measure the blind you're taking down and order the same size. The problem is that a blind is manufactured smaller than the window opening it's ordered for, so it can actually fit inside the frame and clear the mounting brackets. Measuring the old blind gives you the blind's size, not your window's actual opening size, and ordering to that number usually produces a new blind that's too small.
What to do instead: Always measure the window opening itself, frame to frame or drywall to drywall, not the blind currently hanging in it. This holds even if the old blind fit perfectly when it was new.
2. Measuring Only One Location
Windows are rarely perfectly uniform from top to bottom and side to side, even when they look that way. Taking a single width and height measurement misses variation that's often invisible to the eye but very real once you're trying to fit a rigid headrail or frame into the opening.
What to do instead: Measure width at the top, middle, and bottom of the opening, and height at the left, center, and right. Use the smallest of your three width measurements and the largest of your three height measurements when you order. Our guide on measuring bay windows shows just how much this three-point approach matters when a window isn't a simple rectangle.
3. Not Accounting for Depth or Other Obstructions
Width and height get most of the attention, but depth determines whether your product will actually mount the way you expect, and obstructions like a window crank, sash lock, or interior trim can eat into both your depth and your usable width without being obvious at a glance.
What to do instead: Check your window's depth against the product's minimum and flush mounting depth specifications, and look for handles, locks, or trim that could interfere with the headrail or brackets. This matters even more on shallow windows or with no-drill products; our guides on measuring for shallow mount blinds and measuring for no-drill blinds and shades go into detail on exactly what to check.
4. Rounding or Taking Your Own Deductions
Some people round a measurement to the nearest whole or half inch for convenience, or intentionally shave a bit off the width because they assume the blind needs to be smaller than the opening to fit. Both habits cause problems, because custom manufacturing depends on precision, and the deduction has often already been built into how the product is made. For inside mount blinds provide the actual window measurements and we do the rest for the perfect fit.
What to do instead: Give us your window's exact measurement on inside mount, down to the eighth of an inch, with no rounding and no deductions of your own. We take any necessary deductions for mounting clearance and operation at the factory, so submitting your own adjusted number usually results in a blind that ends up smaller than it should be. For outside mount, add for overlap and the blinds will come the size you specify.
5. Assuming Similar-Looking Windows Are the Same Size
Two windows that look identical, even in the same room or the same wall, can differ by enough to matter once you're ordering a custom-fit product. Framing tolerances, settling, and construction variation are common enough that "looks the same" isn't a reliable substitute for an actual measurement.
What to do instead: Measure every window individually, even ones that appear to match. This is especially important when ordering for multiple windows in one room, an entire house, or a multi-unit property, where the temptation to measure once and reuse the number is strongest.
The Five Mistakes at a Glance
| Mistake | What it usually causes | How to avoid it |
|---|---|---|
| Measuring the old blinds | A new blind that's too small for the actual window opening | Measure the window opening itself, not the blind coming down |
| Measuring only one location | A blind that doesn't sit evenly or doesn't fit at the narrowest point | Measure width and height at three points and use the narrowest width, longest height |
| Ignoring depth or obstructions | A product that doesn't mount as expected, or protrudes past the trim | Check depth against product specs and look for handles, locks, and trim |
| Taking your own deductions | A blind that ends up too small once factory deductions are applied on top | Submit your exact window measurement with no rounding or deductions |
| Assuming similar windows match | A blind that fits one window but not a "matching" one nearby | Measure every window individually, even ones that look identical |
Our Take on Measuring Accuracy
Blinds Chalet has been helping customers measure and order custom window blinds and shades since 2006, and these five mistakes account for the large majority of fit issues we help resolve. None of them require special tools or expertise to avoid, just a bit of care and an understanding of why each step matters. If you're ever unsure about a measurement before you order, our design consultants are happy to walk through it with you over the phone.
Related Guides
- How to Measure for Blinds and Shades
- How to Measure Bay Windows for Blinds and Shades
- How to Measure for Shallow Mount Blinds and Shades
- How to Measure for No-Drill Blinds and Shades
Frequently Asked Questions
Why shouldn't I just measure my old blinds when replacing them?
A blind is manufactured smaller than the window opening it's made for, so measuring the old blind gives you the blind's size, not your window's actual opening. Always measure the window opening itself instead.
Do I really need to measure in three places?
Yes. Windows are rarely perfectly uniform, and a single measurement can miss variation that affects fit. Measure width at the top, middle, and bottom, and height at the left, center, and right, then use the smallest width and largest height.
Should I subtract anything from my measurement before ordering?
No. Submit your window's exact measurement with no rounding and no deductions. We take any necessary deductions for mounting clearance and operation at the factory, so adjusting the number yourself typically results in a blind that's too small.
Can I use one measurement for multiple windows that look the same?
It's not recommended. Windows that appear identical can vary slightly due to framing tolerances or settling. Measure each window individually, even in a set that looks uniform.
What obstructions should I check for besides width and height?
Check your window's depth against the product's mounting depth specifications, and look for handles, locks, or trim inside the opening that could interfere with the headrail or brackets once installed.
